If corals can have personalities, then none has a bigger one than the Button, or Meat, coral. These distinctive polyps have skyrocketed in popularity in the last few years, and one look at them will tell you why. Their huge, fleshy polyps are free-living, and come in positively electric combinations of fluorescent colors like green, red, purple, and orange. Also called Doughnut, Open-Brain, Owl, and Cat’s Eye corals, there are actually several species, of multiple genera, that comprise this group of zooxanthellate, Large-Polyped Scleractinians (LPS).

Collectively, the button corals can be grouped together as solitary Mussids. That is, they are solitary polyps of the family Mussidae, and so share common body features. Button corals are characterized by having a singular skeletal corallum shaped like a bowl. The corallum is perforated by radiating septal ridges, which may or may not be sharp, but are usually bumpy or serrated. The appearance of the corallum can be a distinguishing feature between species, but is not visible in healthy animals. Button corals have one large mouth, surrounded by a sizable oral disc. During the day, the edges of the oral disc are folded inward, and the entire coral swells tremendously. Large specimens can exceed 6 or 7 inches in diameter. At night, or in the presence of food, the button will fold out its oral disc to expose a row of short, club-like tentacles.

Button corals are very reactive to feeding time, and generally change shape a number of times throughout the day. When you add the changing faces of these corals to the fact that they are solitary, large, and long-lived, it is no wonder that aquarists become exceedingly attached to them. They are also exceptionally beautiful, and their coloration is complemented by the wonderful variety of textures of their surface flesh. They are eye-catching, centerpiece corals for medium to large aquariums, and you will not regret having one.

Natural Habitat and Ecology:

“Personality” quirks and good looks aside, button corals are very ecologically significant. They have been the subject of much taxonomic debate throughout the years, and for good reason. Solitary mussids are found in both the Indo-pacific and Atlantic regions, and possess similar traits across the board. However, the nomenclature and the genetic relationships between species has been reconsidered a number of times since they were first classified. Originally, solitary mussids were assigned to as many as ten different genera (Acanthophyllia, Cynarina, Homophyllia, Indophyllia, Lithophyllia, Parascolymia, Protolobophyllia, Rhodocyathus, Sclerophyllia, and Scolymia). Current consensus has eliminated all but five genera from the list (Acanthophyllia, Cynarina, Homophyllia, Indophyllia, and Scolymia), but the picture is still not entirely clear. As recently as two years ago, one the most popular aquarium species, Acanthophyllia (=Scolymia=Cynarina) deshayesiana was officially reclassified as Acanthophyllia deshayesiana. The classification goes back to 1854, but misidentification and visual similarities between it and Scolymia spp. button corals resulted in long-standing taxonomic confusion. Like many other solitary mussids, A. deshayesiana is an Indo-pacific species, and it is the lone animal assigned to genus Acanthophyllia. On the other hand, there are at least 5 known Scolymia species, three of which are endemic only to the western Atlantic. In fact, recent genetic testing has demonstrated a sizable difference between Atlantic scleractinians (including Scolymia sp.) and their Pacific counterparts. Thus a division between Atlantic Scolymia and Pacific Scolymia may be forthcoming as well.

In spite of the confusing genetics, button corals possess similarities in body type that lend themselves to homogenous habitat requirements. In other words, their large fleshy polyps and free-living nature limit their potential habitats. They are unlikely to be found in the high energy environments of the reef crest and forereef slope. More often, they are located on the back reef, reef wall, and other lower energy areas. Though photosynthetic, button corals may be found as deep as 100 meters and are capable of eating sizable chunks of meat. They are hardy enough to live in turbid water, under overhangs, and in nearly vertical orientations. At the same time, their sizeable, heavy tissues can be torn in turbulent water, so that may be the most limiting habitat factor.

Of course, to reach the appropriate habitat, button corals need to reproduce. Unfortunately, reproduction is not as prodigious in solitary mussids as it is in other scleractinians. Unlike most other coral species, asexual reproduction is a negligible factor. Instead, they heavily rely upon sexual reproduction. Fascinatingly, some species actually gestate their offspring for up to a month, rather than spew out their gametes for broadcast spawning. Once a larval button polyp settles out of the water column, it attaches itself to hard substrate and begins to grow a corrallum. At some point, the polyp will grow too large for its underdeveloped attachment point, come unattached, and settle into a more appropriate location. The problem with this reproductive scheme is that button corals grow slowly, multiply infrequently, and are easily subject to overcollection.

Aquarium Care:

Caring for button corals is relatively easy. As they are typically found on deep reef walls, it is not surprising that they are tolerant of a range of lighting and water conditions. Moderate to indirect bright lighting will suit them very well, and I have witnessed multiple specimens do equally well beneath both diffuse metal halide and direct T5 fluorescent lighting. Standard reef tank parameters are completely sufficient for button corals, and though they may tolerate some minimal nutrient levels, it is always best to maintain pristine water conditions. Desirable water flow rates are dependant upon species, with Acanthophyllia deshayesiana and Cynarina spp. typically preferring lower water velocities than Scolymia spp.

Considerable thought should be given to the placement of the button coral within the aquarium. Most species will eventually grow into large animals of 6 inches in diameter, or more. Their tissues can be easily damaged by other tank inhabitants, and they topple over if not well-secured. Due to the magnitude of their daily tissue swelling, button corals that are placed precariously or unevenly on the aquascape can easily become dislodged. In spite of the difficulties with this type of placement, acclaimed aquarist and author Julian Sprung (2003) recommends against placing the coral in sand. Doing so risks allowing burrowing animals to damage the coral’s delicate tissues. He instead suggests that they be cemented to rocks in a horizontal, or near-horizontal, manner. This orientation will prevent the animal from being over-turned, along with keeping its skeleton from tearing its own flesh.

Feeding button corals is easy. They readily accept small and large morsels of meat, and have even been known eat pellet foods. Often, buttons will catch food leftover from feeding fish and other livestock. Nonetheless, twice weekly meals of silversides, squid, or shrimp will result in better growth and enhanced coloration. When feeding, one of two methods can be employed to induce tentacle extension. The aquarist can wait until the tank goes into dusk or dark mode, offering the food when the coral opens on its own. Alternatively, the coral can be teased open by a small squirt of squid or clam juice, then fed when the tentacles have expanded.

Though originally thought to be impossible, it seems that some intrepid aquarists have managed to successfully propagate button corals. A recent article by Craig Shimokusu (2009) details his story of a successful attempt to frag a Scolymia australis specimen. Instead of using a rotary tool to cut through the corallum, he employed a diamond band saw to slice the button coral in half through the mouth. The diamond band saw transferred much less heat to the coral, making the process far safer. The cuts were clean and the coral began to recover almost immediately. Evidently the animal was taking food again within one week. If this process can be repeated with regularity, the news is quite exciting because the slow growing, unclonable nature of button corals has led to their overcollection for the aquarium trade.

A button coral is sure to become your favorite coral. Treat them well and they will thrive in your tank. And please remember that these corals are relatively rare, and very special. They should be given VIP status in your reef tank because…frankly…that is what they are. If you decide to go ahead and get one, I can promise you two things—you will name it, and you will love it!

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